With miniaturization of personal computers, video cameras and portable phones, lithium secondary batteries are put to practical use and become widespread as power sources because of high energy density in the devices in the fields of information-related devices and communication devices. In the field of automobiles, there is also urgent demand for development of electric vehicles, because of environment problems and resources problems, and lithium secondary batteries are also examined as power sources for the electric vehicles.
Conventionally, as anode active materials used in lithium secondary batteries, carbon materials such as graphite have been widely used, but the Li storage capacity of the carbon materials is generally low, and thus Sn, Sn alloys etc. that have a higher Li storage capacity than in the carbon materials attract attention.
Patent Document 1 discloses a porous film electrode comprising: a current collector consisting of a material not alloying with Li, and a film consisting of Sn or an Sn-containing alloy and being formed by electroplating on the current collector, wherein the film is a porous film having a specific density. In the Examples therein, it is described that a film of Sn alloy or the like having a film thickness of about 10 μm was formed.
Patent Document 2 discloses an anode material for nonaqueous-electrolyte secondary battery, which uses as an anode material a copper foil electroplated with Sn—Ni and the like. In the Examples therein, it is described that a film of Sn alloy or the like having a film thickness of about 14 to 30 μm was formed.
Patent Document 3 discloses an electrode material for secondary battery, comprising a current collector having a tin- or tin alloy-plated coat formed on one side or both sides thereof by precipitation from a tin or tin-alloy plating bath, wherein the plated coat has formed a coat consisting of substantially continuing plating particles having an average particle size of less than 0.5 μm, and the plated coat has been precipitated from a tin or tin-alloy plating bath having a specific component. In the Examples therein, it is described that a film of Sn alloy or the like having a film thickness of about 2 μm was formed.
On one hand, when a lithium secondary battery for example is applied to automobiles, the lithium secondary battery is required to enable rapid charging. However, even if the lithium secondary batteries etc. described in the Patent Documents mentioned above are used, effective rapid charging are not feasible in some cases.
Patent Document 1: JP-A-2004-139768
Patent Document 2: JP-A-2001-256968
Patent Document 3: JP-A-2003-142088